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Updated Recommendations for Isolation of Persons with Mumps

Mumps, an acute vaccine-preventable viral illness transmitted by respiratory droplets and saliva, has an incubation
period most commonly of 16--18 days. The classic clinical presentation of mumps is parotitis, which can be preceded by several
days of nonspecific prodromal symptoms; however, mumps also can be asymptomatic, especially in young children.
Mumps transmission can occur from persons with subclinical or clinical infections and during the prodromal or symptomatic
phases of illness (1,2). In 2006, during a mumps resurgence in the United States, the latest national recommendations from
CDC and the American Academy of Pediatrics (AAP) stipulated that persons with mumps be maintained in isolation with
standard precautions and droplet precautions for 9 days after onset of parotitis
(3).* However, the existence of conflicting guidance
(i.e., that the infectious period of mumps extended through the fourth day after parotitis
onset) led to confusion regarding
the appropriate length of isolation. In addition, during the 2006 resurgence, compliance with recommendations for isolation
in university settings was substantially lower for 9 days (65%) compared with 4--5 days (86%)
(4). In 2007, after a review of the evidence supporting the 9-day isolation guidance by AAP and CDC, AAP changed its isolation guidance for
health-care workers in ambulatory settings from 9 days to 5 days
(5). In February 2008, after review of data on mumps in
health-care settings, mumps viral load, and mumps virus isolation, the Healthcare Infection Control Practices Advisory
Committee (HICPAC) approved changes in its recommendations related to mumps in in-patient settings. As a result, CDC, AAP,
and HICPAC all now recommend a 5-day period after onset of parotitis, both for isolation of persons with mumps in
either community or health-care settings and for use of standard precautions and droplet precautions. This report summarizes
the scientific basis for these changes in mumps isolation guidance.

To review the scientific evidence underlying the 9-day isolation recommendation, researchers from CDC and AAP
searched available literature for relevant published articles on mumps transmission and mumps in health-care settings. Because
existing data on mumps transmission are scant, the literature review included reports on factors that are considered to be
correlated with mumps transmission risk, including articles on viral isolation and viral load from saliva or respiratory secretions.

Data on viral isolation from saliva or throat swabs were available from eight small studies (median number of subjects:
16; range 1--46). Seven studies were conducted before the availability of mumps vaccine or in countries without a
mumps vaccination program; the eighth study was conducted in the postvaccine era in a community with low vaccination
coverage, and the vaccination status of the mumps patients was not stated. Among the eight studies, although mumps virus was
isolated successfully from 7 days before (6) to 8 days after
(7) onset of parotitis, isolation rates were much greater closer to
parotitis onset. For seven of the eight studies with available data on isolation of mumps virus by day relative to onset of
parotitis, combined data showed that the proportion of samples positive for mumps virus increased from 17% (one of six specimens)
6--7 days before onset of parotitis to 40% (four of 10 specimens) 2--3 days before onset, 86% (six of seven specimens) 1
day before onset, and 78% (seven of nine specimens) on the day of parotitis onset. The data also showed that the proportion
of
samples positive for mumps virus decreased from 81% (29 of 36 specimens) 1 day after parotitis onset to 49% (18 of
37 specimens) 2--3 days after onset, 40% (six of 15 specimens) 4--5 days after onset, and 17% (one of six specimens) 6--7
days after onset of parotitis. In the eighth study, viral identification using reverse transcription--polymerase chain reaction
from buccal specimens from patients with parotitis was conducted during the 2006 mumps outbreak at a U.S. college where
most patients had been vaccinated with 2 doses of measles, mumps, and rubella (MMR) vaccine. The study found that, among
20 patients tested <3 days after onset of parotitis, mumps viral RNA was detected in seven (35%)
(8). A total of 26 specimens from 14 patients tested from 4--22 days after onset of parotitis all were negative for mumps viral RNA. A study from
Japan, examining viral load during the course of natural infection, found that viral load decreased substantially during the first 4
days after illness onset and was extremely low thereafter
(9).

Serious consequences of mumps transmission in health-care settings are rare. This is likely explained by the relatively
low infectiousness and transmission rate of mumps and the fact that hospitalization for mumps is uncommon. Although
mumps transmission from patients to health-care personnel (HCP) in emergency departments occurred during the
1986--1987 mumps outbreaks in Tennessee, most mumps cases among HCP during that period were believed to be acquired in
the community (10). Mumps transmission also has occurred in hospital settings despite prompt isolation of cases after onset
of parotitis, affirming other research indicating that viral shedding occurs before onset of parotitis
(1).

The scientific evidence from the CDC and AAP review indicates that, although mumps virus can be isolated from saliva
or respiratory secretions 5 or more days after parotitis onset, virus most often is isolated before or around the time of onset,
and viral load decreases rapidly during the 4 days after onset of parotitis. Therefore, the risk for transmission after 5 days
is considered low; most transmission likely occurs before onset of parotitis and within the subsequent 5 days. Transmission
also occurs from persons with subclinical infections who are not isolated. A longer isolation period of 9 days likely would result
in less compliance and more cost and not produce any substantial decrease in mumps transmission.

Based on this review, CDC, AAP, and HICPAC now recommend a 5-day period after onset of parotitis for 1) isolation
of persons with mumps in either community or health-care settings and 2) use of standard precautions and droplet
precautions. Postexposure recommendations remain unchanged. HCP with no evidence of mumps immunity who are exposed to
patients with mumps should be excluded from duty from the 12th day after first exposure through the 26th day after last exposure.

The best strategy for preventing mumps in the community and among HCP is promoting high levels of immunity
by vaccination. A 2-dose regimen is currently recommended for all children, with the first MMR vaccine dose administered
at 12--15 months and the second at 4--6 years. Unless they have other evidence of mumps
immunity,§ all school-aged
children, students in post high school institutions (e.g., colleges), international travelers, and HCP also should receive 2 doses of
MMR vaccine. Other adults should receive at least 1 dose of MMR
vaccine.¶ Other methods for decreasing transmission in
the community and health-care settings include 1) isolation of cases, 2) postexposure exclusion from duty of HCP
without evidence of immunity, and 3) use of standard precautions (including respiratory hygiene and cough etiquette)
and transmission-based droplet precautions while caring for patients with mumps.

Bitsko RH, Cortese MM, Dayan GH, et al. Detection of RNA of mumps virus during an outbreak in a population with a high level of
measles, mumps, and rubella vaccine coverage. J Clin Microbiol 2008;46:1101--3.

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